The study suggests that intake of nitrate, found naturally in spinach and other leafy vegetables, is linked to the development of stronger muscles – at doses obtainable from a normal diet. Writing in The Journal of Nutrition, researchers from the Karolinska Institutet, Sweden, reveal findings to suggest that there may be some truth behind the classic cartoon Popeye – who ate spinach to grow his muscles.
"From a nutritional perspective our study is interesting because the amount of nitrate that affected muscle strength in mice was relatively low," said Dr Andrés Hernández – who led the research.
"Translated to humans it means that we can obtain the equivalent volume by eating more of a vegetarian diet, as nitrate is found naturally in several leafy vegetables, especially in beetroot juice, for example,” he said.
While spinach and beetroot are two of the main sources of nitrate, it also occurs naturally in many other leafy vegetables, including as lettuce and chard, said the researchers.
The team divided the mice into two groups, one which was given nitrate in their drinking water for seven days, whilst the other group received a control diet.
The quantity of nitrate that the mice received was roughly equivalent to that which a person would obtain by eating 200 to 300 grams of fresh spinach or two to three beetroots per day, revealed Hernández.
A week into the experiment the team examined different muscles on the mice's legs and feet – finding that those fed nitrate had much stronger muscles. They revealed that the greatest effect was observed in the extensor digitorum longus muscle (which extends down the tibia) and the flexor digitorum brevis muscle (of the foot).
As the study progressed, the team then discovered that nitrate-fed mice had a higher concentration of two proteins in their muscles – which they assume explains the greater muscle strength.
The two proteins – CASQ1 and DHPR – are involved in the homeostasis of calcium, which is an important determinant of muscle contraction.
Hernández and his colleagues now want to take their discoveries further and study how they can be applied to people with muscle weakness.
Source: The Journal of Physiology
Published online ahead of print, doi:10.1113/jphysiol.2012.232777
“Dietary nitrate increases tetanic [Ca2+]iand contractile force in mouse fast-twitch muscle”
Authors: A. Hernández, T. A. Schiffer, N. Ivarsson, A.J. Cheng, J.D. Bruton, J.O. Lundberg, et al